Tectum/js/core/pdf-writer.js

/*!
 * Tectum
 * Copyright © 2026 Machiel Heinen.
 * Alle rechten voorbehouden. Gebruik uitsluitend met schriftelijke toestemming.
 * Zie LICENTIE.md.
 */
// ============================================================
// js/core/pdf-writer.js — minimale, dependency-vrije PDF-generator.
// Schrijft geldige PDF 1.4 bytes rechtstreeks (geen jsPDF: geen
// netwerktoegang om dat te vendoren). Ondersteunt lijnen, rechthoeken,
// tekst (standaard Helvetica, geen embedding nodig) en kleuren, over
// meerdere pagina's. Coordinaten in PDF-punten (1pt = 1/72 inch),
// oorsprong linksonder — precies zoals PDF dat zelf verwacht.
//
// Puur string/byte-opbouw, geen browser-specifieke API's nodig om het
// DOCUMENT te bouwen (alleen het downloaden ervan is browser-specifiek,
// zie savePdfBlob hieronder).
// ============================================================

function createPdfDocument() {
  const objects = [];
  let nextObjId = 1;
  const pageDefs = [];
  let fontId, catalogId, pagesId;

  function newObj(content) {
    const id = nextObjId++;
    objects.push({ id, content });
    return id;
  }

  function fmt(n) {
    return Math.round(n * 100) / 100;
  }

  function escapePdfText(str) {
    return str.replace(/\\/g, '\\\\').replace(/\(/g, '\\(').replace(/\)/g, '\\)');
  }

  function toLatin1(str) {
    let out = '';
    for (let i = 0; i < str.length; i++) {
      const code = str.charCodeAt(i);
      out += code <= 255 ? str[i] : '?';
    }
    return out;
  }

  // Ruwe schatting van Helvetica-tekstbreedte (geen AFM-metrics embedded).
  function estimateTextWidth(str, size) {
    return str.length * size * 0.55;
  }

  fontId = newObj('<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>');

  function addPage(widthPt, heightPt) {
    const ops = [];
    let strokeKey = null, fillKey = null, widthKey = null;

    function setStroke(r, g, b) {
      const key = r + ',' + g + ',' + b;
      if (key === strokeKey) return;
      strokeKey = key;
      ops.push(`${fmt(r)} ${fmt(g)} ${fmt(b)} RG`);
    }
    function setFill(r, g, b) {
      const key = r + ',' + g + ',' + b;
      if (key === fillKey) return;
      fillKey = key;
      ops.push(`${fmt(r)} ${fmt(g)} ${fmt(b)} rg`);
    }
    function setLineWidth(w) {
      if (w === widthKey) return;
      widthKey = w;
      ops.push(`${fmt(w)} w`);
    }
    function line(x1, y1, x2, y2) {
      ops.push(`${fmt(x1)} ${fmt(y1)} m ${fmt(x2)} ${fmt(y2)} l S`);
    }
    function rect(x, y, w, h, mode) {
      ops.push(`${fmt(x)} ${fmt(y)} ${fmt(w)} ${fmt(h)} re ${mode || 'S'}`);
    }
    function polyline(points, close) {
      if (!points.length) return;
      ops.push(`${fmt(points[0][0])} ${fmt(points[0][1])} m`);
      for (let i = 1; i < points.length; i++) ops.push(`${fmt(points[i][0])} ${fmt(points[i][1])} l`);
      ops.push(close ? 's' : 'S');
    }
    function text(x, y, size, str, align) {
      const s = escapePdfText(toLatin1(str));
      let tx = x;
      if (align === 'center') tx = x - estimateTextWidth(str, size) / 2;
      else if (align === 'right') tx = x - estimateTextWidth(str, size);
      ops.push(`BT /F1 ${fmt(size)} Tf ${fmt(tx)} ${fmt(y)} Td (${s}) Tj ET`);
    }
    function textRotated(x, y, size, str, degrees) {
      const rad = (degrees * Math.PI) / 180;
      const cos = Math.cos(rad), sin = Math.sin(rad);
      const s = escapePdfText(toLatin1(str));
      ops.push(`BT /F1 ${fmt(size)} Tf ${fmt(cos)} ${fmt(sin)} ${fmt(-sin)} ${fmt(cos)} ${fmt(x)} ${fmt(y)} Tm (${s}) Tj ET`);
    }

    const contentId = newObj('');
    const pageId = newObj('');
    pageDefs.push({ pageId, contentId, ops, widthPt, heightPt });

    return { setStroke, setFill, setLineWidth, line, rect, polyline, text, textRotated, estimateTextWidth };
  }

  function build() {
    pagesId = newObj('');
    catalogId = newObj(`<< /Type /Catalog /Pages ${pagesId} 0 R >>`);

    pageDefs.forEach(p => {
      const streamBody = p.ops.join('\n');
      objects.find(o => o.id === p.contentId).content =
        `<< /Length ${streamBody.length} >>\nstream\n${streamBody}\nendstream`;
      objects.find(o => o.id === p.pageId).content =
        `<< /Type /Page /Parent ${pagesId} 0 R /MediaBox [0 0 ${fmt(p.widthPt)} ${fmt(p.heightPt)}] ` +
        `/Resources << /Font << /F1 ${fontId} 0 R >> >> /Contents ${p.contentId} 0 R >>`;
    });

    objects.find(o => o.id === pagesId).content =
      `<< /Type /Pages /Kids [${pageDefs.map(p => p.pageId + ' 0 R').join(' ')}] /Count ${pageDefs.length} >>`;

    objects.sort((a, b) => a.id - b.id);

    let out = '%PDF-1.4\n%\xE2\xE3\xCF\xD3\n';
    const offsets = [0];
    objects.forEach(obj => {
      offsets[obj.id] = out.length;
      out += `${obj.id} 0 obj\n${obj.content}\nendobj\n`;
    });

    const xrefOffset = out.length;
    out += `xref\n0 ${objects.length + 1}\n0000000000 65535 f \n`;
    for (let i = 1; i <= objects.length; i++) {
      out += String(offsets[i]).padStart(10, '0') + ' 00000 n \n';
    }
    out += `trailer\n<< /Size ${objects.length + 1} /Root ${catalogId} 0 R >>\nstartxref\n${xrefOffset}\n%%EOF`;

    return out;
  }

  return { addPage, build };
}

// Zet een Latin1-string (elk char = 1 byte, zie hierboven) om naar een
// Blob en start een download. Browser-specifiek, puur I/O — de opbouw
// hierboven is dat niet.
function savePdfBlob(latin1String, filename) {
  const bytes = new Uint8Array(latin1String.length);
  for (let i = 0; i < latin1String.length; i++) bytes[i] = latin1String.charCodeAt(i) & 0xff;
  const blob = new Blob([bytes], { type: 'application/pdf' });
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  URL.revokeObjectURL(url);
}